Solid Electrolytic Capacitor Containing Polyaniline

ABSTRACT

A solid electrolytic capacitor containing a capacitor element is provided. The capacitor element contains a sintered porous anode body, a dielectric that overlies the anode body, a solid electrolyte that overlies the dielectric, and an external polymer coating that overlies the solid electrolyte and includes conductive polymer particles. The solid electrolyte includes a conductive polymer having repeating units derived from an aniline monomer having the following general formula (I):

CROSS REFERENCE TO RELATED APPLICATION

The present application claims filing benefit of U.S. Provisional PatentApplication Ser. No. 62/717,137 having a filing date of Aug. 10, 2018,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) are typicallymade by pressing a metal powder (e.g., tantalum) around a metal leadwire, sintering the pressed part, anodizing the sintered anode, andthereafter applying a solid electrolyte. Intrinsically conductivepolymers are often employed as the solid electrolyte due to theiradvantageous low equivalent series resistance (“ESR”) and“non-burning/non-ignition” failure mode. For example, such electrolytescan be formed through in situ chemical polymerization of a3,4-dioxythiophene monomer (“EDOT”) in the presence of a catalyst anddopant. However, conventional capacitors that employ in situ polymerizedpolymers tend to have a relatively high leakage current (“DCL”) and failat high voltages, such as experienced during a fast switch on oroperational current spike. In an attempt to overcome these issues,dispersions have also been employed that are formed from a complex ofpoly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid(“PEDOT:PSS”). While the PEDOT:PSS dispersions can result in improvedleakage current values, other problems nevertheless remain. For example,one problem with polymer slurry-based capacitors is that they canachieve only a relatively low percentage of their wet capacitance, whichmeans that they have a relatively large capacitance loss and/orfluctuation in the presence of atmosphere humidity.

As such, a need exists for an improved solid electrolytic capacitor thatexhibits relatively stable electrical properties.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a solidelectrolytic capacitor is disclosed that contains a capacitor element.The capacitor element contains a sintered porous anode body, adielectric that overlies the anode body, a solid electrolyte thatoverlies the dielectric, and an external polymer coating that overliesthe solid electrolyte and includes conductive polymer particles. Thesolid electrolyte includes a conductive polymer having repeating unitsderived from an aniline monomer having the following general formula(I):

wherein,

R₅ and R₆ are independently hydrogen, alkyl, alkenyl, aryl, alkoxy,aryloxy, alkylthioalkyl, alkylaryl, arylalkyl, haloalkyl, amino, epoxy,silane, siloxane, alcohol, benzyl, carboxylate, ether, ethercarboxylate, ether sulfonate, ester sulfonate, urethane, or acombination thereof.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a cross-sectional view of one embodiment of a capacitor of theassembly of the present invention;

FIG. 2 is a cross-sectional view of another embodiment of a capacitor ofthe assembly of the present invention;

FIG. 3 is a cross-sectional view of yet another embodiment of acapacitor of the assembly of the present invention; and

FIG. 4 is a top view of still another embodiment of a capacitor of theassembly of the present invention.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a solidelectrolytic capacitor that contains a capacitor element including aporous anode body, dielectric overlying the anode body, solidelectrolyte overlying the dielectric, and an external polymer coatingcontaining conductive polymer particles. To help facilitate the use ofthe capacitor in high voltage applications, the solid electrolyteincludes a conductive polymer containing repeating aniline units of thefollowing general formula (I):

wherein, R₅ and R₆ are independently hydrogen, alkyl, alkenyl, aryl,alkoxy, aryloxy, alkylthioalkyl, alkylaryl, arylalkyl, haloalkyl, amino,epoxy, silane, siloxane, alcohol, benzyl, carboxylate, ether, ethercarboxylate, ether sulfonate, ester sulfonate, urethane, or acombination thereof.

Without intending to be limited by theory, it is believed that suchmaterials can help improve certain electrical properties of theresulting capacitor. The capacitor may, for example, exhibit arelatively high “breakdown voltage” (voltage at which the capacitorfails), such as about 85 volts or more, in some embodiments about 90volts or more, in some embodiments about 95 volts or more, and in someembodiments, from about 100 volts to about 300 volts, such as determinedby increasing the applied voltage in increments of 3 volts until theleakage current reaches 1 mA. Likewise, the capacitor may also be ableto withstand relatively high surge currents, which is also common inhigh voltage applications. The peak surge current may be, for example,about 100 Amps or more, in some embodiments about 200 Amps or more, andin some embodiments, and in some embodiments, from about 300 Amps toabout 800 Amps. The capacitor may also exhibit a high percentage of itswet capacitance, which enables it to have only a small capacitance lossand/or fluctuation in the presence of atmosphere humidity. Thisperformance characteristic is quantified by the “capacitance recovery”,which is determined by the equation:

Recovery=(Dry Capacitance/Wet Capacitance)×100

The capacitor may exhibit a capacitance recovery of about 75% or more,in some embodiments about 80% or more, and in some embodiments, fromabout 85% to 100%. The dry capacitance may be about 1 milliFarad persquare centimeter (“mF/cm²”) or more, in some embodiments about 2 mF/cm²or more, in some embodiments from about 5 to about 50 mF/cm², and insome embodiments, from about 8 to about 20 mF/cm², measured at afrequency of 120 Hz.

The capacitor can also exhibit other improved electrical properties. Forinstance, after being subjected to an applied voltage (e.g., 120 volts)for a period of time from about 30 minutes to about 20 hours, in someembodiments from about 1 hour to about 18 hours, and in someembodiments, from about 4 hours to about 16 hours, the capacitor mayexhibit a leakage current (“DCL”) of only about 100 microamps (“μA”) orless, in some embodiments about 70 μA or less, and in some embodiments,from about 1 to about 50 μA. Notably, the capacitor may exhibit such lowDCL values even under dry conditions, such as described above.

Other electrical properties of the capacitor may also be good and remainstable under various conditions. For example, the capacitor may exhibita relatively low equivalence series resistance (“ESR”), such as about200 mohms, in some embodiments less than about 150 mohms, in someembodiments from about 0.01 to about 125 mohms, and in some embodiments,from about 0.1 to about 100 mohms, measured at an operating frequency of100 kHz and temperature of 23° C. The capacitor may also exhibit a drycapacitance of about 30 nanoFarads per square centimeter (“nF/cm²”) ormore, in some embodiments about 100 nF/cm² or more, in some embodimentsfrom about 200 to about 3,000 nF/cm², and in some embodiments, fromabout 400 to about 2,000 nF/cm², measured at a frequency of 120 Hz attemperature of 23° C. Notably, such electrical properties (e.g., ESRand/or capacitance) can still remain stable even at high temperaturesand/or dry conditions as noted above. For example, the capacitor mayexhibit an ESR and/or capacitance value within the ranges noted aboveeven after being exposed to a temperature of from about 80° C. or more,in some embodiments from about 100° C. to about 150° C., and in someembodiments, from about 105° C. to about 130° C. (e.g., 105° C. or 125°C.) fora substantial period of time, such as for about 100 hours ormore, in some embodiments from about 150 hours to about 3000 hours, andin some embodiments, from about 200 hours to about 2500 hours (e.g., 240hours). In one embodiment, for example, the ratio of the ESR and/orcapacitance value of the capacitor after being exposed to the hightemperature (e.g., 125° C.) for 240 hours to the initial ESR and/orcapacitance value of the capacitor (e.g., at 23° C.) is about 2.0 orless, in some embodiments about 1.5 or less, and in some embodiments,from 1.0 to about 1.3.

It is also believed that the dissipation factor of the capacitor may bemaintained at relatively low levels. The dissipation factor generallyrefers to losses that occur in the capacitor and is usually expressed asa percentage of the ideal capacitor performance. For example, thedissipation factor of the capacitor is typically about 250% or less, insome embodiments about 200% or less, and in some embodiments, from about1% to about 180%, as determined at a frequency of 120 Hz.

Various embodiments of the capacitor will now be described in moredetail.

I. Capacitor Element

A. Anode Body

The capacitor element includes an anode that contains a dielectricformed on a sintered porous body. The porous anode body may be formedfrom a powder that contains a valve metal (i.e., metal that is capableof oxidation) or valve metal-based compound, such as tantalum, niobium,aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitridesthereof, and so forth. The powder is typically formed from a reductionprocess in which a tantalum salt (e.g., potassium fluorotantalate(K₂TaF₇), sodium fluorotantalate (Na₂TaF₇), tantalum pentachloride(TaCl₅), etc.) is reacted with a reducing agent. The reducing agent maybe provided in the form of a liquid, gas (e.g., hydrogen), or solid,such as a metal (e.g., sodium), metal alloy, or metal salt. In oneembodiment, for instance, a tantalum salt (e.g., TaCl₅) may be heated ata temperature of from about 900° C. to about 2,000° C., in someembodiments from about 1,000° C. to about 1,800° C., and in someembodiments, from about 1,100° C. to about 1,600° C., to form a vaporthat can be reduced in the presence of a gaseous reducing agent (e.g.,hydrogen). Additional details of such a reduction reaction may bedescribed in WO 2014/199480 to Maeshima, et al. After the reduction, theproduct may be cooled, crushed, and washed to form a powder.

The specific charge of the powder typically varies from about 2,000 toabout 600,000 microFarads*Volts per gram (“μF*V/g”) depending on thedesired application. For instance, in certain embodiments, a high chargepowder may be employed that has a specific charge of from about 100,000to about 600,000 μF*V/g, in some embodiments from about 120,000 to about500,000 μF*V/g, and in some embodiments, from about 150,000 to about400,000 μF*V/g. In other embodiments, a low charge powder may beemployed that has a specific charge of from about 2,000 to about 100,000μF*V/g, in some embodiments from about 5,000 to about 80,000 μF*V/g, andin some embodiments, from about 10,000 to about 70,000 μF*V/g. As isknown in the art, the specific charge may be determined by multiplyingcapacitance by the anodizing voltage employed, and then dividing thisproduct by the weight of the anodized electrode body.

The powder may be a free-flowing, finely divided powder that containsprimary particles. The primary particles of the powder generally have amedian size (D50) of from about 5 to about 500 nanometers, in someembodiments from about 10 to about 400 nanometers, and in someembodiments, from about 20 to about 250 nanometers, such as determinedusing a laser particle size distribution analyzer made by BECKMANCOULTER Corporation (e.g., LS-230), optionally after subjecting theparticles to an ultrasonic wave vibration of 70 seconds. The primaryparticles typically have a three-dimensional granular shape (e.g.,nodular or angular). Such particles typically have a relatively low“aspect ratio”, which is the average diameter or width of the particlesdivided by the average thickness (“D/T”). For example, the aspect ratioof the particles may be about 4 or less, in some embodiments about 3 orless, and in some embodiments, from about 1 to about 2. In addition toprimary particles, the powder may also contain other types of particles,such as secondary particles formed by aggregating (or agglomerating) theprimary particles. Such secondary particles may have a median size (D50)of from about 1 to about 500 micrometers, and in some embodiments, fromabout 10 to about 250 micrometers.

Agglomeration of the particles may occur by heating the particles and/orthrough the use of a binder. For example, agglomeration may occur at atemperature of from about 0° C. to about 40° C., in some embodimentsfrom about 5° C. to about 35° C., and in some embodiments, from about15° C. to about 30° C. Suitable binders may likewise include, forinstance, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol);poly(vinyl pyrollidone); cellulosic polymers, such ascarboxymethylcellulose, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, and methylhydroxyethyl cellulose; atactic polypropylene,polyethylene; polyethylene glycol (e.g., Carbowax from Dow ChemicalCo.); polystyrene, poly(butadiene/styrene); polyamides, polyimides, andpolyacrylamides, high molecular weight polyethers; copolymers ofethylene oxide and propylene oxide; fluoropolymers, such aspolytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefincopolymers; acrylic polymers, such as sodium polyacrylate, poly(loweralkyl acrylates), poly(lower alkyl methacrylates) and copolymers oflower alkyl acrylates and methacrylates; and fatty acids and waxes, suchas stearic and other soapy fatty acids, vegetable wax, microwaxes(purified paraffins), etc.

The resulting powder may be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead, which may bein the form of a wire, sheet, etc. The lead may extend in a longitudinaldirection from the anode body and may be formed from any electricallyconductive material, such as tantalum, niobium, aluminum, hafnium,titanium, etc., as well as electrically conductive oxides and/ornitrides of thereof. Connection of the lead to the anode body may alsobe accomplished using other known techniques, such as by welding thelead to the body or embedding it within the anode body during formation(e.g., prior to compaction and/or sintering).

Any binder may be removed after pressing by heating the pellet undervacuum at a certain temperature (e.g., from about 150° C. to about 500°C.) for several minutes. Alternatively, the binder may also be removedby contacting the pellet with an aqueous solution, such as described inU.S. Pat. No. 6,197,252 to Bishop, et al. Thereafter, the pellet issintered to form a porous, integral mass. The pellet is typicallysintered at a temperature of from about 700° C. to about 1800° C., insome embodiments from about 800° C. to about 1700° C., and in someembodiments, from about 900° C. to about 1400° C., for a time of fromabout 5 minutes to about 100 minutes, and in some embodiments, fromabout 8 minutes to about 15 minutes. This may occur in one or moresteps. If desired, sintering may occur in an atmosphere that limits thetransfer of oxygen atoms to the anode. For example, sintering may occurin a reducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc.The reducing atmosphere may be at a pressure of from about 10 Torr toabout 2000 Torr, in some embodiments from about 100 Torr to about 1000Torr, and in some embodiments, from about 100 Torr to about 930 Torr.Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may alsobe employed.

B. Dielectric

The anode is also coated with a dielectric. As indicated above, thedielectric is formed by anodically oxidizing (“anodizing”) the sinteredanode so that a dielectric layer is formed over and/or within the anode.For example, a tantalum (Ta) anode may be anodized to tantalum pentoxide(Ta₂O₅).

Typically, anodization is performed by initially applying an electrolyteto the anode, such as by dipping anode into the electrolyte. Theelectrolyte is generally in the form of a liquid, such as a solution(e.g., aqueous or non-aqueous), dispersion, melt, etc. A solvent isgenerally employed in the electrolyte, such as water (e.g., deionizedwater); ethers (e.g., diethyl ether and tetrahydrofuran); glycols (e.g.,ethylene glycol, propylene glycol, etc.); alcohols (e.g., methanol,ethanol, n-propanol, isopropanol, and butanol); triglycerides; ketones(e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters(e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate,and methoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); and so forth. The solvent(s) mayconstitute from about 50 wt. % to about 99.9 wt. %, in some embodimentsfrom about 75 wt. % to about 99 wt. %, and in some embodiments, fromabout 80 wt. % to about 95 wt. % of the electrolyte. Although notnecessarily required, the use of an aqueous solvent (e.g., water) isoften desired to facilitate formation of an oxide. In fact, water mayconstitute about 1 wt. % or more, in some embodiments about 10 wt. % ormore, in some embodiments about 50 wt. % or more, in some embodimentsabout 70 wt. % or more, and in some embodiments, about 90 wt. % to 100wt. % of the solvent(s) used in the electrolyte.

The electrolyte is electrically conductive and may have an electricalconductivity of about 1 milliSiemens per centimeter (“mS/cm”) or more,in some embodiments about 30 mS/cm or more, and in some embodiments,from about 40 mS/cm to about 100 mS/cm, determined at a temperature of25° C. To enhance the electrical conductivity of the electrolyte, anionic compound is generally employed that is capable of dissociating inthe solvent to form ions. Suitable ionic compounds for this purpose mayinclude, for instance, acids, such as nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.;organic acids, including carboxylic acids, such as acrylic acid,methacrylic acid, malonic acid, succinic acid, salicylic acid,sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleic acid,gallic acid, tartaric acid, citric acid, formic acid, acetic acid,glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalicacid, glutaric acid, gluconic acid, lactic acid, aspartic acid,glutaminic acid, itaconic acid, trifluoroacetic acid, barbituric acid,cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid,etc.; sulfonic acids, such as methanesulfonic acid, benzenesulfonicacid, toluenesulfonic acid, trifluoromethanesulfonic acid,styrenesulfonic acid, naphthalene disulfonic acid,hydroxybenzenesulfonic acid, dodecylsulfonic acid,dodecylbenzenesulfonic acid, etc.; polymeric acids, such aspoly(acrylic) or poly(methacrylic) acid and copolymers thereof (e.g.,maleic-acrylic, sulfonic-acrylic, and styrene-acrylic copolymers),carageenic acid, carboxymethyl cellulose, alginic acid, etc.; and soforth. The concentration of ionic compounds is selected to achieve thedesired electrical conductivity. For example, an acid (e.g., phosphoricacid) may constitute from about 0.01 wt. % to about 5 wt. %, in someembodiments from about 0.05 wt. % to about 0.8 wt. %, and in someembodiments, from about 0.1 wt. % to about 0.5 wt. % of the electrolyte.If desired, blends of ionic compounds may also be employed in theelectrolyte.

To form the dielectric, a current is typically passed through theelectrolyte while it is in contact with the anode body. The value of theformation voltage manages the thickness of the dielectric layer. Forexample, the power supply may be initially set up at a galvanostaticmode until the required voltage is reached. Thereafter, the power supplymay be switched to a potentiostatic mode to ensure that the desireddielectric thickness is formed over the entire surface of the anode. Ofcourse, other known methods may also be employed, such as pulse or steppotentiostatic methods. The voltage at which anodic oxidation occurstypically ranges from about 4 to about 250 V, and in some embodiments,from about 5 to about 200 V, and in some embodiments, from about 10 toabout 150 V. During oxidation, the electrolyte can be kept at anelevated temperature, such as about 30° C. or more, in some embodimentsfrom about 40° C. to about 200° C., and in some embodiments, from about50° C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode in that itpossesses a first portion that overlies an external surface of the anodeand a second portion that overlies an interior surface of the anode. Insuch embodiments, the first portion is selectively formed so that itsthickness is greater than that of the second portion. It should beunderstood, however, that the thickness of the dielectric layer need notbe uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20. To form a dielectric layerhaving a differential thickness, a multi-stage process may be employed.In each stage of the process, the sintered anode is anodically oxidized(“anodized”) to form a dielectric layer (e.g., tantalum pentoxide).During the first stage of anodization, a relatively small formingvoltage is typically employed to ensure that the desired dielectricthickness is achieved for the inner region, such as forming voltagesranging from about 1 to about 90 volts, in some embodiments from about 2to about 50 volts, and in some embodiments, from about 5 to about 20volts. Thereafter, the sintered body may then be anodically oxidized ina second stage of the process to increase the thickness of thedielectric to the desired level. This is generally accomplished byanodizing in an electrolyte at a higher voltage than employed during thefirst stage, such as at forming voltages ranging from about 50 to about350 volts, in some embodiments from about 60 to about 300 volts, and insome embodiments, from about 70 to about 200 volts. During the firstand/or second stages, the electrolyte may be kept at a temperaturewithin the range of from about 15° C. to about 95° C., in someembodiments from about 20° C. to about 90° C., and in some embodiments,from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however,the electrolyte employed during at least one stage of the dielectricdevelopment process contains an ionic compound as explained above. Inone particular embodiment, it may be desired that the electrolyteemployed in the second stage has a lower ionic conductivity than theelectrolyte employed in the first stage to prevent a significant amountof oxide film from forming on the internal surface of anode. In thisregard, the electrolyte employed during the first stage may contain anionic compound that is an acid, such as nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.Such an electrolyte may have an electrical conductivity of from about0.1 to about 100 mS/cm, in some embodiments from about 0.2 to about 20mS/cm, and in some embodiments, from about 1 to about 10 mS/cm,determined at a temperature of 25° C. The electrolyte employed duringthe second stage may likewise contain an ionic compound that is a saltof a weak acid so that the hydronium ion concentration increases in thepores as a result of charge passage therein. Ion transport or diffusionis such that the weak acid anion moves into the pores as necessary tobalance the electrical charges. As a result, the concentration of theprincipal conducting species (hydronium ion) is reduced in theestablishment of equilibrium between the hydronium ion, acid anion, andundissociated acid, thus forms a poorer-conducting species. Thereduction in the concentration of the conducting species results in arelatively high voltage drop in the electrolyte, which hinders furtheranodization in the interior while a thicker oxide layer, is being builtup on the outside to a higher formation voltage in the region ofcontinued high conductivity. Suitable weak acid salts may include, forinstance, ammonium or alkali metal salts (e.g., sodium, potassium, etc.)of boric acid, boronic acid, acetic acid, oxalic acid, lactic acid,adipic acid, etc. Particularly suitable salts include sodium tetraborateand ammonium pentaborate. Such electrolytes typically have an electricalconductivity of from about 0.1 to about 20 mS/cm, in some embodimentsfrom about 0.5 to about 10 mS/cm, and in some embodiments, from about 1to about 5 mS/cm, determined at a temperature of 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode may also be rinsed or washed with another solvent (e.g., water)after the first and/or second stages to remove the electrolyte.

C. Solid Electrolyte

A solid electrolyte overlies the dielectric and generally functions asthe cathode for the capacitor. Typically, the total thickness of thesolid electrolyte is from about 1 to about 50 μm, and in someembodiments, from about 5 to about 20 μm. As indicated above, the solidelectrolyte contains a conductive polymer having repeating units derivedfrom an aniline monomer having the following general formula (I):

wherein,

R₅ and R₆ are independently hydrogen, alkyl (e.g., methyl, ethyl, hexyl,octyl, etc.), alkenyl, aryl, alkoxy (e.g., methoxy, ethoxy, etc.),aryloxy (e.g., phenoxy), alkylthioalkyl, alkylaryl, arylalkyl, haloalkyl(e.g., trifluoromethyl), amino, epoxy, silane, siloxane, alcohol,benzyl, carboxylate, ether, ether carboxylate, ether sulfonate, estersulfonate, urethane, etc., or a combination thereof. In particularembodiments, for instance, R₅ and R₆ are hydrogen such that theconductive polymer contains repeating units derived from aniline. Inother embodiments, one or both of R₅ or R₆ may be an alkyl group (e.g.,methyl) or alkoxy group (e.g., methoxy). The polyaniline typically has aweight-average molecular weight of about 20,000 grams per mole or more,in some embodiments from about 50,000 to 500,000 grams per mole, and insome embodiments, from about 60,000 to about 300,000 grams per mole,such as determined by a polystyrene-converted value measured by gelpermeation chromatography.

The aniline polymers derived from the monomer of formula (I) aregenerally considered to be “extrinsically” conductive to the extent thatthey typically require the presence of a dopants. In certainembodiments, for instance, the aniline monomer may be polymerized in acomposition that also contains a proton donor, which can thus act as aninternal dopant for the polymer. Such proton donors are typicallyemployed in an amount of from about 0.1 to about 0.5 moles, in someembodiments from about 0.3 to about 0.45 moles, and in some embodiments,from about 0.3 to about 0.4 moles per mole of the aniline monomer.Suitable proton donors may include, for instance, Bronsted acids orsalts thereof, and particularly organic acids and/or salts thereof. Inone embodiment, for instance, the proton donor may be an organic acidcompound, such as those having the following general formula (II):

wherein,

m is an integer from 1 to 10 (e.g., 1 or 2);

M is hydrogen; an organic free radical group, such as an aromaticcompound, (e.g., pyridium, imidazolium, anilinium, etc.); an inorganicfree radical group, such as an alkali metal (e.g., lithium, sodium,potassium, etc.), alkaline earth metal (e.g., calcium, magnesium, etc.),transition metal (e.g., iron), ammonium, etc.; and so forth;

X is an anion, such as SO₃ ⁻, PO₃ ²⁻, PO4_((OH)) ⁻, OPO₃ ²⁻, OPO₂(OH)⁻,COO⁻, etc.;

R⁴, R⁵, and R⁶ are independently hydrogen; a hydrocarbon group, such asa straight-chain or branched C₁-C₂₄ alkyl (e.g., octyl or 2-ethylhexyl),cycloalkyl, aryl (e.g., pentyl), alkylaryl, etc.; or a R⁹ ₃Si— group,wherein R⁹ are each independently hydrogen or a hydrocarbon group; and

R⁷ and R⁸ are independently a hydrocarbon group, such as astraight-chain or branched C₁-C24 alkyl (e.g., butyl, octyl, decyl, or2-ethylhexyl), cycloalkyl, aryl (e.g., pentyl), alkylaryl, etc.; or—(R¹⁰O)_(q)—R¹¹, wherein q is an integer equal to 1 or more (e.g., 1 to10), R¹⁰ is a hydrocarbon group or a silylene group, R¹¹ is hydrogen,hydrocarbon group, or R¹² ₃Si—, wherein R¹² are each independently ahydrocarbon group.

In one particular embodiment, for instance, X may be SO₃, R⁴ may behydrogen, R⁵ may be hydrogen, and/or R⁶ may be hydrogen. In suchembodiments, R⁷ and/or R⁸ may, for instance, be a straight-chain orbranched C₁-C₂₄ alkyl, such as butyl, octyl, decyl, or 2-ethylhexyl. Forinstance, one particularly suitable proton donor is sodiumdi-2-ethylhexylsulfosuccinate.

The conductive polymer may be formed through a variety of techniques aswould be understood by those skilled in the art. In one particularembodiment, for example, a polyaniline derived from the general formula(I) may be polymerized in a composition that contains an oxidativecatalyst. Derivatives of these monomers may also be employed that are,for example, dimers or trimers of the above compounds. The derivativesmay be made up of identical or different monomer units and used in pureform and in a mixture with one another and/or with the monomers.Oxidized or reduced forms of these precursors may also be employed. Theamount of the oxidizing catalyst used in this polymerization reaction isnot particularly limited, and may be within a range of from 1 to 50molar times, more preferably from 1 to 20 molar times to the number ofmoles of the aniline monomer used as a material charged. The oxidativecatalyst may be a transition metal salt, such as a salt of an inorganicor organic acid that contain ammonium, sodium, gold, iron(III),copper(II), chromium(VI), cerium(IV), manganese(IV), manganese(VII), orruthenium(III) cations. Particularly suitable transition metal saltsinclude halides (e.g., FeCl₃ or HAuCl₄); salts of other inorganic acids(e.g., Fe(ClO₄)₃, Fe₂(SO₄)₃, (NH₄)₂S₂O₈, or Na₃Mo₁₂PO₄₀); and salts oforganic acids and inorganic acids comprising organic radicals. Examplesof salts of inorganic acids with organic radicals include, for instance,iron(III) salts of sulfuric acid monoesters of C₁ to C₂₀ alkanols (e.g.,iron(III) salt of lauryl sulfate). Likewise, examples of salts oforganic acids include, for instance, iron(III) salts of C₁ to C₂₀ alkanesulfonic acids (e.g., methane, ethane, propane, butane, or dodecanesulfonic acid); iron (III) salts of aliphatic perfluorosulfonic acids(e.g., trifluoromethane sulfonic acid, perfluorobutane sulfonic acid, orperfluorooctane sulfonic acid); iron (III) salts of aliphatic C₁ to C₂₀carboxylic acids (e.g., 2-ethylhexylcarboxylic acid); iron (III) saltsof aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acid orperfluorooctane acid); iron (III) salts of aromatic sulfonic acidsoptionally substituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonicacid, o-toluene sulfonic acid, p-toluene sulfonic acid, ordodecylbenzene sulfonic acid); iron (III) salts of cycloalkane sulfonicacids (e.g., camphor sulfonic acid); and so forth. Mixtures of theseabove-mentioned salts may also be used.

In addition to monomers and other optional components (e.g., protondonor, catalyst, etc.), the polymerization composition also typicallycontains one or more solvents, such as described in U.S. Pat. No.9,754,697, which is incorporated herein in its entirety by referencethereto. Suitable solvents may include, for instance, water, glycols(e.g., ethylene glycol, propylene glycol, butylene glycol, triethyleneglycol, hexylene glycol, polyethylene glycols, ethoxydiglycol,dipropyleneglycol, etc.); glycol ethers (e.g., methyl glycol ether,ethyl glycol ether, isopropyl glycol ether, etc.); alcohols (e.g.,methanol, ethanol, n-propanol, iso-propanol, and butanol); ketones(e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters(e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate,methoxypropyl acetate, ethylene carbonate, propylene carbonate, etc.);amides (e.g., dimethylformamide, dimethylacetamide,dimethylcaprylic/capric fatty acid amide and N-alkylpyrrolidones);sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO) and sulfolane);phenolic compounds (e.g., toluene, xylene, etc.), and so forth. Incertain cases, multiple solvents may be employed, such as water and anorganic solvent (e.g., toluene). The amount of the solvent used in thispolymerization reaction is not particularly limited so long as theaniline monomer used as a material is dissolved in the solvent, however,it is preferably from 0.1 to 100 times, more preferably from 0.1 to 50times the weight of the aniline monomer charged. The temperature atwhich the reaction occurs typically varies from about −20° C. to about140° C., and in some embodiments, from about 20° C. to about 100° C.Upon completion of the reaction, known purification techniques may beemployed to remove any salt impurities, such by washing with a solvent,re-precipitation, centrifugal sedimentation, ultrafiltration, dialysisor ion exchange resin treatment, etc., as well as combination thereof.

Of course, other components may also be employed in the polymerizationcomposition to enhance the properties of the resulting solidelectrolyte. For example, an inorganic acid (e.g., phosphoric acid,sulfuric acid, etc.) may be employed in certain embodiments. Likewise,an emulsifier can be employed to help minimize the risk of phaseinversion during polymerization. Suitable emulsifiers may include, forinstance, ionic emulsifiers and nonionic emulsifiers as are known in theart.

As indicated above, aniline polymers derived from the monomer of formula(I) are generally considered to be “extrinsically” conductive to theextent that they typically require the presence of a dopant. In additionto or in lieu of the internal dopants discussed above, it is alsopossible to employ an external dopant in the solid electrolyte thatforms a complex or composite with the polyaniline after it is formed.One example of such an external dopant is a phenolic compound. Whenemployed, such phenolic compounds are typically employed in an amount inan amount of from about 10 to about 60 grams, in some embodiments fromabout 15 to about 50 grams, and in some embodiments, from about 20 toabout 40 grams per gram of the polyaniline. Suitable phenolic compoundsmay include a hydroxphenolic compound, such those having one of thefollowing structures (III), (IV), (V), or (VI):

wherein,

-   -   n is an integer of 0 to 5, preferably 0 to 3 (e.g., 0 or 1); and

R is independently a C₁-C₂₀ alkyl, alkenyl, cycloalkyl, aryl, alkylaryl,etc.

Specific examples of the hydroxyphenolic compound of the formula (III)may include methoxyphenol, ethoxyphenol, propoxyphenol,isopropoxyphenol, butyloxyphenol, isobutyloxyphenol, andtert-butyloxyphenol. A specific example of the hydroxyphenolic compoundof the formula (IV) may include hydroxynaphthalene. Specific examples ofthe hydroxyphenolic compound of formula (V) may include cresol,ethylphenol, propylphenol (e.g. 4-isopropylphenol), butylphenol, andpentylphenol (e.g. 4-tert-pentylphenol). Likewise, specific examples ofthe hydroxyphenolic compound of formula (VI) may include1,6-naphthanediol, 2,6-naphthalenediol, and 2,7-naphthalenediol.

If desired, a heat stabilizer may also be employed in the solidelectrolyte. When employed, such heat stabilizers are typically employedin an amount in an amount of from about 10 to about 60 grams, in someembodiments from about 15 to about 50 grams, and in some embodiments,from about 20 to about 40 grams per gram of the polyaniline. Suitableheat stabilizers include, for instance, organic acids, inorganic acids,and/or salts thereof. For instance, suitable heat stabilizers mayinclude organic sulfonic acids, such as alkylsulfonic acids (e.g.,methanesulfonic acid, ethanesulfonic acid, di-2-ethylhexylsulfosuccinicacid, etc.) and aromatic sulfonic acids (e.g., benzenesulfonic acid,naphthalenesulfonic acid, anthracenesulfonic acid,dodecylbenzenesulfonic acid, anthraquinonesulfonic acid, etc.); organiccarboxylic acids, such as alkylcarboxylic acids (e.g., undecylenic acid,cyclohexane carboxylic acid, 2-ethyihexanoic acid, etc.) and aromaticcarboxylic acids (e.g., salicylic acid, benzoic acid, naphthoic acid,trimesic acid, etc.); organic phosphoric acids, such as alkylphosphoricacids (e.g., dodecylphosphoric acid, bis(2-ethylhexyl)hydrogenphosphate, etc.) and aromatic phosphoric acids; organic phosphonicacids, such as alkylphosphonic acids and aromatic phosphonic acids(e.g., benzenephosphonic acid, naphthalenephosphonic acid,phenylphosphonic acid, etc.); and so forth, as well as salts of any ofthe foregoing.

The resulting polyaniline able to readily impregnate the small poresformed by the high specific charge powder, so that the resulting solidelectrolyte has a “film-like” configuration and coats at least a portionof the anode in a substantially uniform manner. This improves thequality of the resulting oxide as well as its surface coverage, andthereby enhances the electrical properties of the capacitor assembly.

i. Inner Layers

The solid electrolyte is generally formed from one or more “inner”conductive polymer layers. The term “inner” in this context refers toone or more layers formed from the same material and that overly thedielectric, whether directly or via another layer (e.g., adhesivelayer). One or multiple inner layers may be employed. For example, thesolid electrolyte typically contains from 2 to 30, in some embodimentsfrom 4 to 20, and in some embodiments, from about 5 to 15 inner layers(e.g., 10 layers).

In one embodiment, the inner layer(s) may contain a polyaniline such asdescribed above. In one particular embodiment, the inner layer(s) aregenerally free of other types of conductive polymers and thus formedprimarily from the polyaniline described herein. More particularly,polyaniline may constitute about 50 wt. % or more, in some embodimentsabout 70 wt. % or more, and in some embodiments, about 90 wt. % or more(e.g., 100 wt. %) of the inner layer(s). In another embodiment, theinner layer(s) may contain a conductive polymer other than polyaniline(e.g., thiophene polymer), as described in more detail below.Regardless, the inner layer(s) are typically applied in the form of asolution containing a solvent. The concentration of the conductivepolymer may vary depending on the desired viscosity of and theparticular manner in which the layer is to be applied to the anode.Typically, however, the polymer constitutes from about 0.1 to about 10wt. %, in some embodiments from about 0.4 to about 5 wt. %, and in someembodiments, from about 0.5 to about 4 wt. % of the solution. Solvent(s)may likewise constitute from about 90 wt. % to about 99.9 wt. %, in someembodiments from about 95 wt. % to about 99.6 wt. %, and in someembodiments, from about 96 wt. % to about 99.5 wt. % of the solution.When employed, a solution may be applied to the anode using any knowntechnique, such as dipping, casting (e.g., curtain coating, spincoating, etc.), printing (e.g., gravure printing, offset printing,screen printing, etc.), and so forth. The resulting conductive polymerlayer may be dried and/or washed after it is applied to the anode.

ii. Outer Layers

The solid electrolyte may contain only “inner layers” so that it isessentially formed from the same material, i.e., polyaniline.Nevertheless, in other embodiments, the solid electrolyte may alsocontain one or more optional “outer” conductive polymer layers that areformed from a different material than the inner layer(s) and overly theinner layer(s). One or multiple outer layers may be employed. Forexample, the solid electrolyte may contain from 2 to 30, in someembodiments from 4 to 20, and in some embodiments, from about 5 to 15outer layers.

In one embodiment, the outer layer(s) may be formed from other types ofpolyanilines or other types of conductive polymers, such aspolypyrroles, polythiophenes, etc. For example, the outer layer(s) areformed primarily from such conductive polymers in that they constituteabout 50 wt. % or more, in some embodiments about 70 wt. % or more, andin some embodiments, about 90 wt. % or more (e.g., 100 wt. %) of arespective outer layer. In another embodiment, the outer layer(s) may beformed from a polyaniline as described above. For example, the outerlayer(s) may be formed primarily from such polyanilines in that theyconstitute about 50 wt. % or more, in some embodiments about 70 wt. % ormore, and in some embodiments, about 90 wt. % or more (e.g., 100 wt. %)of a respective outer layer.

When employing other types of conductive polymers in the inner and/orouter layers, various polymers may be employed. For instance, athiophene polymer may be employed that has repeating units of thefollowing formula (VII):

wherein,

R₇ is a linear or branched, C₁ to C18 alkyl radical (e.g., methyl,ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl, n-pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl,1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl,n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); C₅ to C₁₂cycloalkyl radical (e.g., cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl, cyclodecyl, etc.); C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); C₇ to C₁₈ aralkyl radical (e.g., benzyl, o-,m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-xylyl, mesityl, etc.); C₁to C₄ hydroxyalkyl radical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0. In one particular embodiment, “q” is 0 and thepolymer is poly(3,4-ethylenedioxythiophene). One commercially suitableexample of a monomer suitable for forming such a polymer is3,4-ethylenedioxthiophene, which is available from Heraeus under thedesignation Clevios™ M.

The polymers of formula (VII) are generally considered to be“extrinsically” conductive to the extent that they require the presenceof a separate counterion that is not covalently bound to the polymer.The counterion may be a monomeric or polymeric anion that counteractsthe charge of the conductive polymer. Polymeric anions can, for example,be anions of polymeric carboxylic acids (e.g., polyacrylic acids,polymethacrylic acid, polymaleic acids, etc.); polymeric sulfonic acids(e.g., polystyrene sulfonic acids (“PSS”), polyvinyl sulfonic acids,etc.); and so forth. The acids may also be copolymers, such ascopolymers of vinyl carboxylic and vinyl sulfonic acids with otherpolymerizable monomers, such as acrylic acid esters and styrene.Likewise, suitable monomeric anions include, for example, anions of C₁to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonic acid); aliphaticperfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid or perfluorooctane sulfonic acid);aliphatic C₁ to C₂₀ carboxylic acids (e.g., 2-ethyl-hexylcarboxylicacid); aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acidor perfluorooctanoic acid); aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid or dodecylbenzenesulfonic acid); cycloalkane sulfonic acids (e.g., camphor sulfonic acidor tetrafluoroborates, hexafluorophosphates, perchlorates,hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates);and so forth. Particularly suitable counteranions are polymeric anions,such as a polymeric carboxylic or sulfonic acid (e.g., polystyrenesulfonic acid (“PSS”)). The molecular weight of such polymeric anionstypically ranges from about 1,000 to about 2,000,000, and in someembodiments, from about 2,000 to about 500,000.

Intrinsically conductive polymers may also be employed that have apositive charge located on the main chain that is at least partiallycompensated by anions covalently bound to the polymer. For example, oneexample of a suitable intrinsically conductive thiophene polymer mayhave repeating units of the following formula (VIII):

wherein,

R is (CH₂)_(a)—O—(CH₂)_(b);

a is from 0 to 10, in some embodiments from 0 to 6, and in someembodiments, from 1 to 4 (e.g., 1);

b is from 1 to 18, in some embodiments from 1 to 10, and in someembodiments, from 2 to 6 (e.g., 2, 3, 4, or 5);

Z is an anion, such as SO₃ ⁻, C(O)O⁻, BF₄ ⁻, CF₃SO₃ ⁻, SbF₆ ⁻,N(SO₂CF₃)₂ ⁻, C₄H₃O₄ ⁻, ClO₄ ⁻, etc.;

X is a cation, such as hydrogen, an alkali metal (e.g., lithium, sodium,rubidium, cesium or potassium), ammonium, etc.

In one particular embodiment, Z in formula (II) is a sulfonate ion suchthat the intrinsically conductive polymer contains repeating units ofthe following formula (IX):

wherein, R and X are defined above. In formula (II) or (III), a ispreferably 1 and b is preferably 3 or 4. Likewise, X is preferablysodium or potassium.

If desired, the polymer may be a copolymer that contains other types ofrepeating units. In such embodiments, the repeating units of formula(VIII) typically constitute about 50 mol. % or more, in some embodimentsfrom about 75 mol. % to about 99 mol. %, and in some embodiments, fromabout 85 mol. % to about 95 mol. % of the total amount of repeatingunits in the copolymer. Of course, the polymer may also be a homopolymerto the extent that it contains 100 mol. % of the repeating units offormula (VIII). Specific examples of such homopolymers includepoly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-1-butane-sulphonicacid, salt) andpoly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-1-propanesulphonicacid, salt).

When employed, it may be desirable that the conductive polymer isapplied in the form of a dispersion of pre-polymerized conductiveparticles. Such particles typically have an average size (e.g.,diameter) of from about 1 to about 100 nanometers, in some embodimentsfrom about 2 to about 80 nanometers, and in some embodiments, from about4 to about 50 nanometers. The diameter of the particles may bedetermined using known techniques, such as by ultracentrifuge, laserdiffraction, etc. The shape of the particles may likewise vary. In oneparticular embodiment, for instance, the particles are spherical inshape. However, it should be understood that other shapes are alsocontemplated by the present invention, such as plates, rods, discs,bars, tubes, irregular shapes, etc. The concentration of the particlesin the dispersion may vary depending on the desired viscosity of thedispersion and the particular manner in which the dispersion is to beapplied to the capacitor element. Typically, however, the particlesconstitute from about 0.1 to about 10 wt. %, in some embodiments fromabout 0.4 to about 5 wt. %, and in some embodiments, from about 0.5 toabout 4 wt. % of the dispersion.

The dispersion may also contain one or more binders to further enhancethe adhesive nature of the polymeric layer and also increase thestability of the particles within the dispersion. The binders may beorganic in nature, such as polyvinyl alcohols, polyvinyl pyrrolidones,polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates,polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acidesters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylicacid ester, vinyl acetate/acrylic acid ester and ethylene/vinyl acetatecopolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers,polyesters, polycarbonates, polyurethanes, polyamides, polyimides,polysulfones, melamine formaldehyde resins, epoxide resins, siliconeresins or celluloses. Crosslinking agents may also be employed toenhance the adhesion capacity of the binders. Such crosslinking agentsmay include, for instance, melamine compounds, masked isocyanates orfunctional silanes, such as 3-glycidoxypropyltrialkoxysilane,tetraethoxysilane and tetraethoxysilane hydrolysate or crosslinkablepolymers, such as polyurethanes, polyacrylates or polyolefins, andsubsequent crosslinking.

Dispersion agents may also be employed to facilitate the ability toapply the layer to the anode. Suitable dispersion agents includesolvents, such as aliphatic alcohols (e.g., methanol, ethanol,i-propanol and butanol), aliphatic ketones (e.g., acetone and methylethyl ketones), aliphatic carboxylic acid esters (e.g., ethyl acetateand butyl acetate), aromatic hydrocarbons (e.g., toluene and xylene),aliphatic hydrocarbons (e.g., hexane, heptane and cyclohexane),chlorinated hydrocarbons (e.g., dichloromethane and dichloroethane),aliphatic nitriles (e.g., acetonitrile), aliphatic sulfoxides andsulfones (e.g., dimethyl sulfoxide and sulfolane), aliphatic carboxylicacid amides (e.g., methylacetamide, dimethylacetamide anddimethylformamide), aliphatic and araliphatic ethers (e.g., diethyletherand anisole), water, and mixtures of any of the foregoing solvents. Aparticularly suitable dispersion agent is water.

In addition to those mentioned above, still other ingredients may alsobe used in the dispersion. For example, conventional fillers may be usedthat have a size of from about 10 nanometers to about 100 micrometers,in some embodiments from about 50 nanometers to about 50 micrometers,and in some embodiments, from about 100 nanometers to about 30micrometers. Examples of such fillers include calcium carbonate,silicates, silica, calcium or barium sulfate, aluminum hydroxide, glassfibers or bulbs, wood flour, cellulose powder carbon black, electricallyconductive polymers, etc. The fillers may be introduced into thedispersion in powder form, but may also be present in another form, suchas fibers.

Surface-active substances may also be employed in the dispersion, suchas ionic or non-ionic surfactants. Furthermore, adhesives may beemployed, such as organofunctional silanes or their hydrolysates, forexample 3-glycidoxypropyltrialkoxysilane, 3-aminopropyl-triethoxysilane, 3-mercaptopropyl-trimethoxysilane,3-metacryloxypropyltrimethoxysilane, vinyltrimethoxysilane oroctyltriethoxysilane. The dispersion may also contain additives thatincrease conductivity, such as ether group-containing compounds (e.g.,tetrahydrofuran), lactone group-containing compounds (e.g.,γ-butyrolactone or γ-valerolactone), amide or lactam group-containingcompounds (e.g., caprolactam, N-methylcaprolactam,N,N-dimethylacetamide, N-methylacetamide, N,N-dimethylformamide (DMF),N-methylformamide, N-methylformanilide, N-methylpyrrolidone (NMP),N-octylpyrrolidone, or pyrrolidone), sulfones and sulfoxides (e.g.,sulfolane (tetramethylenesulfone) or dimethylsulfoxide (DMSO)), sugar orsugar derivatives (e.g., saccharose, glucose, fructose, or lactose),sugar alcohols (e.g., sorbitol or mannitol), furan derivatives (e.g.,2-furancarboxylic acid or 3-furancarboxylic acid), an alcohols (e.g.,ethylene glycol, glycerol, di- or triethylene glycol).

The dispersion may be applied using a variety of known techniques, suchas by spin coating, impregnation, pouring, dropwise application,injection, spraying, doctor blading, brushing, printing (e.g., ink-jet,screen, or pad printing), or dipping. The viscosity of the dispersion istypically from about 0.1 to about 100,000 mPas (measured at a shear rateof 100 s⁻¹), in some embodiments from about 1 to about 10,000 mPas, insome embodiments from about 10 to about 1,500 mPas, and in someembodiments, from about 100 to about 1000 mPas.

If desired, a hydroxyl-functional nonionic polymer may also be employedin the outer layer(s) of the solid electrolyte. The term“hydroxy-functional” generally means that the compound contains at leastone hydroxyl functional group or is capable of possessing such afunctional group in the presence of a solvent. Without intending to belimited by theory, it is believed that the use of a hydroxy-functionalpolymer with a certain molecular weight can minimize the likelihood ofchemical decomposition at high voltages. For instance, the molecularweight of the hydroxy-functional polymer may be from about 100 to 10,000grams per mole, in some embodiments from about 200 to 2,000, in someembodiments from about 300 to about 1,200, and in some embodiments, fromabout 400 to about 800.

Any of a variety of hydroxy-functional nonionic polymers may generallybe employed for this purpose. In one embodiment, for example, thehydroxy-functional polymer is a polyalkylene ether. Polyalkylene ethersmay include polyalkylene glycols (e.g., polyethylene glycols,polypropylene glycols polytetramethylene glycols, polyepichlorohydrins,etc.), polyoxetanes, polyphenylene ethers, polyether ketones, and soforth. Polyalkylene ethers are typically predominantly linear, nonionicpolymers with terminal hydroxy groups. Particularly suitable arepolyethylene glycols, polypropylene glycols and polytetramethyleneglycols (polytetrahydrofurans), which are produced by polyaddition ofethylene oxide, propylene oxide or tetrahydrofuran onto water. Thepolyalkylene ethers may be prepared by polycondensation reactions fromdiols or polyols. The diol component may be selected, in particular,from saturated or unsaturated, branched or unbranched, aliphaticdihydroxy compounds containing 5 to 36 carbon atoms or aromaticdihydroxy compounds, such as, for example, pentane-1,5-diol,hexane-1,6-diol, neopentyl glycol, bis-(hydroxymethyl)-cyclohexanes,bisphenol A, dimer diols, hydrogenated dimer diols or even mixtures ofthe diols mentioned. In addition, polyhydric alcohols may also be usedin the polymerization reaction, including for example glycerol, di- andpolyglycerol, trim ethylolpropane, pentaerythritol or sorbitol.

In addition to those noted above, other hydroxy-functional nonionicpolymers may also be employed in the present invention. Some examples ofsuch polymers include, for instance, ethoxylated alkylphenols;ethoxylated or propoxylated C₆-C₂₄ fatty alcohols; polyoxyethyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₂H₄)₁₋₂₅—OH (e.g., octaethylene glycol monododecylether and pentaethylene glycol monododecyl ether); polyoxypropyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₃H₆)₁₋₂₅—OH; polyoxyethylene glycol octylphenolethers having the following general formula:C₈H₁₇—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., Triton™ X-100); polyoxyethyleneglycol alkylphenol ethers having the following general formula:C₉H₁₉—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., nonoxynol-9); polyoxyethylene glycolesters of C₈-C₂₄ fatty acids, such as polyoxyethylene glycol sorbitanalkyl esters (e.g., polyoxyethylene (20) sorbitan monolaurate,polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20)sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, PEG-20methyl glucose distearate, PEG-20 methyl glucose sesquistearate, PEG-80castor oil, and PEG-20 castor oil, PEG-3 castor oil, PEG 600 dioleate,and PEG 400 dioleate) and polyoxyethylene glycerol alkyl esters (e.g.,polyoxyethylene-23 glycerol laurate and polyoxyethylene-20 glycerolstearate); polyoxyethylene glycol ethers of C₈-C₂₄ fatty acids (e.g.,polyoxyethylene-10 cetyl ether, polyoxyethylene-10 stearyl ether,polyoxyethylene-20 cetyl ether, polyoxyethylene-10 oleyl ether,polyoxyethylene-20 oleyl ether, polyoxyethylene-20 isohexadecyl ether,polyoxyethylene-15 tridecyl ether, and polyoxyethylene-6 tridecylether); block copolymers of polyethylene glycol and polypropylene glycol(e.g., Poloxamers); and so forth, as well as mixtures thereof.

The hydroxy-functional nonionic polymer may be incorporated into theouter layers in a variety of different ways. In certain embodiments, forinstance, the nonionic polymer may simply be incorporated into thedispersion of extrinsically conductive polymers. In such embodiments,the concentration of the nonionic polymer in the layer may be from about1 wt. % to about 50 wt. %, in some embodiments from about 5 wt. % toabout 40 wt. %, and in some embodiments, from about 10 wt. % to about 30wt. %. In other embodiments, however, the nonionic polymer may beapplied after the initial outer layer(s) are formed. In suchembodiments, the technique used to apply the nonionic polymer may vary.For example, the nonionic polymer may be applied in the form of a liquidsolution using various methods, such as immersion, dipping, pouring,dripping, injection, spraying, spreading, painting or printing, forexample, inkjet, screen printing or tampon printing. Solvents known tothe person skilled in the art can be employed in the solution, such aswater, alcohols, or a mixture thereof. The concentration of the nonionicpolymer in such a solution typically ranges from about 5 wt. % to about95 wt. %, in some embodiments from about 10 wt. % to about 70 wt. %, andin some embodiments, from about 15 wt. % to about 50 wt. % of thesolution. If desired, such solutions may be generally free of conductivepolymers. For example, conductive polymers may constitute about 2 wt. %or less, in some embodiments about 1 wt. % or less, and in someembodiments, about 0.5 wt. % or less of the solution.

D. External Polymer Coating

As indicated above, an external polymer coating is also applied to theanode that overlies the solid electrolyte. The external polymer coatinggenerally contains one or more layers formed from conductive polymerparticles, such as described above (e.g., formed from an extrinsicallyconductive polymer). The external coating may be able to furtherpenetrate into the edge region of the capacitor body to increase theadhesion to the dielectric and result in a more mechanically robustpart, which may reduce equivalent series resistance and leakage current.Because it is generally intended to improve the degree of edge coveragerather to impregnate the interior of the anode body, the particles usedin the external coating typically have a larger size than those employedin any optional particles employed in the solid electrolyte (e.g., inthe outer layer(s)). For example, the ratio of the average size of theparticles employed in the external polymer coating to the average sizeof any particles employed in the solid electrolyte is typically fromabout 1.5 to about 30, in some embodiments from about 2 to about 20, andin some embodiments, from about 5 to about 15. For example, theparticles employed in the external coating may have an average size offrom about 50 to about 800 nanometers, in some embodiments from about 80to about 600 nanometers, and in some embodiments, from about 100 toabout 500 nanometers.

A crosslinking agent may also be optionally employed in the externalpolymer coating to further enhance the degree of adhesion to the solidelectrolyte. Typically, the crosslinking agent is applied prior toapplication of the dispersion used in the external coating. Suitablecrosslinking agents are described, for instance, in U.S. PatentPublication No. 2007/0064376 to Merker, et al. and include, forinstance, amines (e.g., diamines, triamines, oligomer amines,polyamines, etc.); polyvalent metal cations, such as salts or compoundsof Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphoniumcompounds, sulfonium compounds, etc. Particularly suitable examplesinclude, for instance, 1,4-diaminocyclohexane,1,4-bis(amino-methyl)cyclohexane, ethylenediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,4-butanediamine, etc., as well as mixturesthereof.

The crosslinking agent is typically applied from a solution ordispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, insome embodiments, from 3 to 6, as determined at 25° C. Acidic compoundsmay be employed to help achieve the desired pH level. Examples ofsolvents or dispersants for the crosslinking agent include water ororganic solvents, such as alcohols, ketones, carboxylic esters, etc. Thecrosslinking agent may be applied to the capacitor body by any knownprocess, such as spin-coating, impregnation, casting, dropwiseapplication, spray application, vapor deposition, sputtering,sublimation, knife-coating, painting or printing, for example inkjet,screen or pad printing. Once applied, the crosslinking agent may bedried prior to application of the polymer dispersion. This process maythen be repeated until the desired thickness is achieved. For example,the total thickness of the entire external polymer coating, includingthe crosslinking agent and dispersion layers, may range from about 1 toabout 50 μm, in some embodiments from about 2 to about 40 μm, and insome embodiments, from about 5 to about 20 μm.

E. Cathode Coating

If desired, the capacitor element may also employ a cathode coating thatoverlies the solid electrolyte and external polymer coating. The cathodecoating may contain a metal particle layer includes a plurality ofconductive metal particles dispersed within a polymer matrix. Theparticles typically constitute from about 50 wt. % to about 99 wt. %, insome embodiments from about 60 wt. % to about 98 wt. %, and in someembodiments, from about 70 wt. % to about 95 wt. % of the layer, whilethe polymer matrix typically constitutes from about 1 wt. % to about 50wt. %, in some embodiments from about 2 wt. % to about 40 wt. %, and insome embodiments, from about 5 wt. % to about 30 wt. % of the layer.

The conductive metal particles may be formed from a variety of differentmetals, such as copper, nickel, silver, nickel, zinc, tin, lead, copper,aluminum, molybdenum, titanium, iron, zirconium, magnesium, etc., aswell as alloys thereof. Silver is a particularly suitable conductivemetal for use in the layer. The metal particles often have a relativelysmall size, such as an average size of from about 0.01 to about 50micrometers, in some embodiments from about 0.1 to about 40 micrometers,and in some embodiments, from about 1 to about 30 micrometers.Typically, only one metal particle layer is employed, although it shouldbe understood that multiple layers may be employed if so desired. Thetotal thickness of such layer(s) is typically within the range of fromabout 1 μm to about 500 μm, in some embodiments from about 5 μm to about200 μm, and in some embodiments, from about 10 μm to about 100 μm.

The polymer matrix typically includes a polymer, which may bethermoplastic or thermosetting in nature. Typically, however, thepolymer is selected so that it can act as a barrier to electromigrationof silver ions, and also so that it contains a relatively small amountof polar groups to minimize the degree of water adsorption in thecathode coating. In this regard, the present inventors have found thatvinyl acetal polymers are particularly suitable for this purpose, suchas polyvinyl butyral, polyvinyl formal, etc. Polyvinyl butyral, forinstance, may be formed by reacting polyvinyl alcohol with an aldehyde(e.g., butyraldehyde). Because this reaction is not typically complete,polyvinyl butyral will generally have a residual hydroxyl content. Byminimizing this content, however, the polymer can possess a lesserdegree of strong polar groups, which would otherwise result in a highdegree of moisture adsorption and result in silver ion migration. Forinstance, the residual hydroxyl content in polyvinyl acetal may be about35 mol. % or less, in some embodiments about 30 mol. % or less, and insome embodiments, from about 10 mol. % to about 25 mol. %. Onecommercially available example of such a polymer is available fromSekisui Chemical Co., Ltd. under the designation “BH-S” (polyvinylbutyral).

To form the cathode coating, a conductive paste is typically applied tothe capacitor that overlies the solid electrolyte. One or more organicsolvents are generally employed in the paste. A variety of differentorganic solvents may generally be employed, such as glycols (e.g.,propylene glycol, butylene glycol, triethylene glycol, hexylene glycol,polyethylene glycols, ethoxydiglycol, and dipropyleneglycol); glycolethers (e.g., methyl glycol ether, ethyl glycol ether, and isopropylglycol ether); ethers (e.g., diethyl ether and tetrahydrofuran);alcohols (e.g., benzyl alcohol, methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones (e.g., acetone,methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); etc., as well as mixtures thereof. Theorganic solvent(s) typically constitute from about 10 wt. % to about 70wt. %, in some embodiments from about 20 wt. % to about 65 wt. %, and insome embodiments, from about 30 wt. % to about 60 wt. %. of the paste.Typically, the metal particles constitute from about 10 wt. % to about60 wt. %, in some embodiments from about 20 wt. % to about 45 wt. %, andin some embodiments, from about 25 wt. % to about 40 wt. % of the paste,and the resinous matrix constitutes from about 0.1 wt. % to about 20 wt.%, in some embodiments from about 0.2 wt. % to about 10 wt. %, and insome embodiments, from about 0.5 wt. % to about 8 wt. % of the paste.

The paste may have a relatively low viscosity, allowing it to be readilyhandled and applied to a capacitor element. The viscosity may, forinstance, range from about 50 to about 3,000 centipoise, in someembodiments from about 100 to about 2,000 centipoise, and in someembodiments, from about 200 to about 1,000 centipoise, such as measuredwith a Brookfield DV-1 viscometer (cone and plate) operating at a speedof 10 rpm and a temperature of 25° C. If desired, thickeners or otherviscosity modifiers may be employed in the paste to increase or decreaseviscosity. Further, the thickness of the applied paste may also berelatively thin and still achieve the desired properties. For example,the thickness of the paste may be from about 0.01 to about 50micrometers, in some embodiments from about 0.5 to about 30 micrometers,and in some embodiments, from about 1 to about 25 micrometers. Onceapplied, the metal paste may be optionally dried to remove certaincomponents, such as the organic solvents. For instance, drying may occurat a temperature of from about 20° C. to about 150° C., in someembodiments from about 50° C. to about 140° C., and in some embodiments,from about 80° C. to about 130° C.

F. Other Components

If desired, the capacitor may also contain other layers as is known inthe art. In certain embodiments, for instance, a carbon layer (e.g.,graphite) may be positioned between the solid electrolyte and the silverlayer that can help further limit contact of the silver layer with thesolid electrolyte. In addition, a pre-coat layer may also be employedthat overlies the dielectric and includes an organometallic compound.

II. Terminations

Once formed, the capacitor element may be provided with terminations,particularly when employed in surface mounting applications. Forexample, the capacitor may contain an anode termination to which ananode lead of the capacitor element is electrically connected and acathode termination to which the cathode of the capacitor element iselectrically connected. Any conductive material may be employed to formthe terminations, such as a conductive metal (e.g., copper, nickel,silver, nickel, zinc, tin, palladium, lead, copper, aluminum,molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof).Particularly suitable conductive metals include, for instance, copper,copper alloys (e.g., copper-zirconium, copper-magnesium, copper-zinc, orcopper-iron), nickel, and nickel alloys (e.g., nickel-iron). Thethickness of the terminations is generally selected to minimize thethickness of the capacitor. For instance, the thickness of theterminations may range from about 0.05 to about 1 millimeter, in someembodiments from about 0.05 to about 0.5 millimeters, and from about0.07 to about 0.2 millimeters. One exemplary conductive material is acopper-iron alloy metal plate available from Wieland (Germany). Ifdesired, the surface of the terminations may be electroplated withnickel, silver, gold, tin, etc. as is known in the art to ensure thatthe final part is mountable to the circuit board. In one particularembodiment, both surfaces of the terminations are plated with nickel andsilver flashes, respectively, while the mounting surface is also platedwith a tin solder layer.

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination and anodetermination. To attach the electrolytic capacitor element to the leadframe, a conductive adhesive may initially be applied to a surface ofthe cathode termination. The conductive adhesive may include, forinstance, conductive metal particles contained with a resin composition.The metal particles may be silver, copper, gold, platinum, nickel, zinc,bismuth, etc. The resin composition may include a thermoset resin (e.g.,epoxy resin), curing agent (e.g., acid anhydride), and coupling agent(e.g., silane coupling agents). Suitable conductive adhesives may bedescribed in U.S. Patent Application Publication No. 2006/0038304 toOsako, et al. Any of a variety of techniques may be used to apply theconductive adhesive to the cathode termination. Printing techniques, forinstance, may be employed due to their practical and cost-savingbenefits. The anode lead may also be electrically connected to the anodetermination using any technique known in the art, such as mechanicalwelding, laser welding, conductive adhesives, etc. Upon electricallyconnecting the anode lead to the anode termination, the conductiveadhesive may then be cured to ensure that the electrolytic capacitorelement is adequately adhered to the cathode termination.

III. Housing

The capacitor element may be incorporated within a housing in variousways. In certain embodiments, for instance, the capacitor element may beenclosed within a case, which may then be filled with a resinousmaterial, such as a thermoset resin (e.g., epoxy resin) that can becured to form a hardened housing. The resinous material may surround andencapsulate the capacitor element so that at least a portion of theanode and cathode terminations are exposed for mounting onto a circuitboard. When encapsulated in this manner, the capacitor element andresinous material form an integral capacitor.

Of course, in alternative embodiments, it may be desirable to enclosethe capacitor element within a housing that remains separate anddistinct. In this manner, the atmosphere of the housing can beselectively controlled so that it is dry, which limits the degree ofmoisture that can contact the capacitor element. For example, themoisture content of the atmosphere (expressed in terms of relativehumidity) may be about 10% or less, in some embodiments about 5% orless, in some embodiments about 3% or less, and in some embodiments,from about 0.001 to about 1%. For example, the atmosphere may be gaseousand contain at least one inert gas, such as nitrogen, helium, argon,xenon, neon, krypton, radon, and so forth, as well as mixtures thereof.Typically, inert gases constitute the majority of the atmosphere withinthe housing, such as from about 50 wt. % to 100 wt. %, in someembodiments from about 75 wt. % to 100 wt. %, and in some embodiments,from about 90 wt. % to about 99 wt. % of the atmosphere. If desired, arelatively small amount of non-inert gases may also be employed, such ascarbon dioxide, oxygen, water vapor, etc. In such cases, however, thenon-inert gases typically constitute 15 wt. % or less, in someembodiments 10 wt. % or less, in some embodiments about 5 wt. % or less,in some embodiments about 1 wt. % or less, and in some embodiments, fromabout 0.01 wt. % to about 1 wt. % of the atmosphere within the housing.

Any of a variety of different materials may be used to form the housing,such as metals, plastics, ceramics, and so forth. In one embodiment, forexample, the housing includes one or more layers of a metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver,steel (e.g., stainless), alloys thereof (e.g., electrically conductiveoxides), composites thereof (e.g., metal coated with electricallyconductive oxide), and so forth. In another embodiment, the housing mayinclude one or more layers of a ceramic material, such as aluminumnitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,glass, etc., as well as combinations thereof.

The housing may have any desired shape, such as cylindrical, D-shaped,rectangular, triangular, prismatic, etc. Referring to FIG. 1, forexample, one embodiment of a capacitor 100 is shown that contains ahousing 122 and a capacitor element 120. In this particular embodiment,the housing 122 is generally rectangular. Typically, the housing and thecapacitor element have the same or similar shape so that the capacitorelement can be readily accommodated within the interior cavity. In theillustrated embodiment, for example, both the capacitor element 120 andthe housing 122 have a generally rectangular shape.

If desired, the capacitor of the present invention may exhibit arelatively high volumetric efficiency. To facilitate such highefficiency, the capacitor element typically occupies a substantialportion of the volume of an interior cavity of the housing. For example,the capacitor element may occupy about 30 vol.% or more, in someembodiments about 50 vol.% or more, in some embodiments about 60 vol.%or more, in some embodiments about 70 vol.% or more, in some embodimentsfrom about 80 vol.% to about 98 vol.%, and in some embodiments, fromabout 85 vol.% to 97 vol.% of the interior cavity of the housing. Tothis end, the difference between the dimensions of the capacitor elementand those of the interior cavity defined by the housing are typicallyrelatively small.

Referring to FIG. 1, for example, the capacitor element 120 may have alength (excluding the length of the anode lead 6) that is relativelysimilar to the length of an interior cavity 126 defined by the housing122. For example, the ratio of the length of the anode to the length ofthe interior cavity ranges from about 0.40 to 1.00, in some embodimentsfrom about 0.50 to about 0.99, in some embodiments from about 0.60 toabout 0.99, and in some embodiments, from about 0.70 to about 0.98. Thecapacitor element 120 may have a length of from about 5 to about 10millimeters, and the interior cavity 126 may have a length of from about6 to about 15 millimeters. Similarly, the ratio of the height of thecapacitor element 120 (in the −z direction) to the height of theinterior cavity 126 may range from about 0.40 to 1.00, in someembodiments from about 0.50 to about 0.99, in some embodiments fromabout 0.60 to about 0.99, and in some embodiments, from about 0.70 toabout 0.98. The ratio of the width of the capacitor element 120 (in the−x direction) to the width of the interior cavity 126 may also rangefrom about 0.50 to 1.00, in some embodiments from about 0.60 to about0.99, in some embodiments from about 0.70 to about 0.99, in someembodiments from about 0.80 to about 0.98, and in some embodiments, fromabout 0.85 to about 0.95. For example, the width of the capacitorelement 120 may be from about 2 to about 7 millimeters and the width ofthe interior cavity 126 may be from about 3 to about 10 millimeters, andthe height of the capacitor element 120 may be from about 0.5 to about 2millimeters and the width of the interior cavity 126 may be from about0.7 to about 6 millimeters.

Although by no means required, the capacitor element may be attached tothe housing in such a manner that an anode termination and cathodetermination are formed external to the housing for subsequentintegration into a circuit. The particular configuration of theterminations may depend on the intended application. In one embodiment,for example, the capacitor may be formed so that it is surfacemountable, and yet still mechanically robust. For example, the anodelead may be electrically connected to external, surface mountable anodeand cathode terminations (e.g., pads, sheets, plates, frames, etc.).Such terminations may extend through the housing to connect with thecapacitor. The thickness or height of the terminations is generallyselected to minimize the thickness of the capacitor. For instance, thethickness of the terminations may range from about 0.05 to about 1millimeter, in some embodiments from about 0.05 to about 0.5millimeters, and from about 0.1 to about 0.2 millimeters. If desired,the surface of the terminations may be electroplated with nickel,silver, gold, tin, etc. as is known in the art to ensure that the finalpart is mountable to the circuit board. In one particular embodiment,the termination(s) are deposited with nickel and silver flashes,respectively, and the mounting surface is also plated with a tin solderlayer. In another embodiment, the termination(s) are deposited with thinouter metal layers (e.g., gold) onto a base metal layer (e.g., copperalloy) to further increase conductivity.

In certain embodiments, connective members may be employed within theinterior cavity of the housing to facilitate connection to theterminations in a mechanically stable manner. For example, referringagain to FIG. 1, the capacitor 100 may include a connection member 162that is formed from a first portion 167 and a second portion 165. Theconnection member 162 may be formed from conductive materials similar tothe external terminations. The first portion 167 and second portion 165may be integral or separate pieces that are connected together, eitherdirectly or via an additional conductive element (e.g., metal). In theillustrated embodiment, the second portion 165 is provided in a planethat is generally parallel to a lateral direction in which the lead 6extends (e.g., −y direction). The first portion 167 is “upstanding” inthe sense that it is provided in a plane that is generally perpendicularthe lateral direction in which the lead 6 extends. In this manner, thefirst portion 167 can limit movement of the lead 6 in the horizontaldirection to enhance surface contact and mechanical stability duringuse. If desired, an insulative material 7 (e.g., Teflon™ washer) may beemployed around the lead 6.

The first portion 167 may possess a mounting region (not shown) that isconnected to the anode lead 6. The region may have a “U-shape” forfurther enhancing surface contact and mechanical stability of the lead6. Connection of the region to the lead 6 may be accomplished using anyof a variety of known techniques, such as welding, laser welding,conductive adhesives, etc. In one particular embodiment, for example,the region is laser welded to the anode lead 6. Regardless of thetechnique chosen, however, the first portion 167 can hold the anode lead6 in substantial horizontal alignment to further enhance the dimensionalstability of the capacitor 100.

Referring again to FIG. 1, one embodiment of the present invention isshown in which the connective member 162 and capacitor element 120 areconnected to the housing 122 through anode and cathode terminations 127and 129, respectively. More specifically, the housing 122 of thisembodiment includes an outer wall 123 and two opposing sidewalls 124between which a cavity 126 is formed that includes the capacitor element120. The outer wall 123 and sidewalls 124 may be formed from one or morelayers of a metal, plastic, or ceramic material such as described above.In this particular embodiment, the anode termination 127 contains afirst region 127 a that is positioned within the housing 122 andelectrically connected to the connection member 162 and a second region127 b that is positioned external to the housing 122 and provides amounting surface 201. Likewise, the cathode termination 129 contains afirst region 129 a that is positioned within the housing 122 andelectrically connected to the solid electrolyte of the capacitor element120 and a second region 129 b that is positioned external to the housing122 and provides a mounting surface 203. It should be understood thatthe entire portion of such regions need not be positioned within orexternal to the housing. In the illustrated embodiment, a conductivetrace 127 c extends in the outer wall 123 of the housing to connect thefirst region 127 a and second region 127 b. Similarly, a conductivetrace 129 c extends in the outer wall 123 of the housing to connect thefirst region 127 a and second region 127 b. The conductive traces and/orregions of the terminations may be separate or integral. In addition toextending through the outer wall of the housing, the traces may also bepositioned at other locations, such as external to the outer wall. Ofcourse, the present invention is by no means limited to the use ofconductive traces for forming the desired terminations.

Regardless of the particular configuration employed, connection of theterminations 127 and 129 to the capacitor element 120 may be made usingany known technique, such as welding, laser welding, conductiveadhesives, etc. In one particular embodiment, for example, a conductiveadhesive 131 is used to connect the second portion 165 of the connectionmember 162 to the anode termination 127. Likewise, a conductive adhesive133 is used to connect the cathode of the capacitor element 120 to thecathode termination 129.

Optionally, a polymeric restraint may also be disposed in contact withone or more surfaces of the capacitor element, such as the rear surface,front surface, upper surface, lower surface, side surface(s), or anycombination thereof. The polymeric restraint can reduce the likelihoodof delamination by the capacitor element from the housing. In thisregard, the polymeric restraint may possesses a certain degree ofstrength that allows it to retain the capacitor element in a relativelyfixed positioned even when it is subjected to vibrational forces, yet isnot so strong that it cracks. For example, the restraint may possess atensile strength of from about 1 to about 150 Megapascals (“MPa”), insome embodiments from about 2 to about 100 MPa, in some embodiments fromabout 10 to about 80 MPa, and in some embodiments, from about 20 toabout 70 MPa, measured at a temperature of about 25° C. It is normallydesired that the restraint is not electrically conductive. Referringagain to FIG. 1, for instance, one embodiment is shown in which a singlepolymeric restraint 197 is disposed in contact with an upper surface 181and rear surface 177 of the capacitor element 120. While a singlerestraint is shown in FIG. 1, it should be understood that separaterestraints may be employed to accomplish the same function. In fact,more generally, any number of polymeric restraints may be employed tocontact any desired surface of the capacitor element. When multiplerestraints are employed, they may be in contact with each other orremain physically separated. For example, in one embodiment, a secondpolymeric restraint (not shown) may be employed that contacts the uppersurface 181 and front surface 179 of the capacitor element 120. Thefirst polymeric restraint 197 and the second polymeric restraint (notshown) may or may not be in contact with each other. In yet anotherembodiment, a polymeric restraint may also contact a lower surface 183and/or side surface(s) of the capacitor element 120, either inconjunction with or in lieu of other surfaces.

Regardless of how it is applied, it is typically desired that thepolymeric restraint is also in contact with at least one surface of thehousing to help further mechanically stabilize the capacitor elementagainst possible delamination. For example, the restraint may be incontact with an interior surface of one or more sidewall(s), outer wall,lid, etc. In FIG. 1, for example, the polymeric restraint 197 is incontact with an interior surface 107 of sidewall 124 and an interiorsurface 109 of outer wall 123. While in contact with the housing, it isnevertheless desired that at least a portion of the cavity defined bythe housing remains unoccupied to allow for the inert gas to flowthrough the cavity and limit contact of the solid electrolyte withoxygen. For example, at least about 5% of the cavity volume typicallyremains unoccupied by the capacitor element and polymer restraint, andin some embodiments, from about 10% to about 50% of the cavity volume.

Once connected in the desired manner, the resulting package ishermetically sealed as described above. Referring again to FIG. 1, forinstance, the housing 122 may also include a lid 125 that is placed onan upper surface of side walls 124 after the capacitor element 120 andthe polymer restraint 197 are positioned within the housing 122. The lid125 may be formed from a ceramic, metal (e.g., iron, copper, nickel,cobalt, etc., as well as alloys thereof), plastic, and so forth. Ifdesired, a sealing member 187 may be disposed between the lid 125 andthe side walls 124 to help provide a good seal. In one embodiment, forexample, the sealing member may include a glass-to-metal seal, Kovar®ring (Goodfellow Camridge, Ltd.), etc. The height of the side walls 124is generally such that the lid 125 does not contact any surface of thecapacitor element 120 so that it is not contaminated. The polymericrestraint 197 may or may not contact the lid 125. When placed in thedesired position, the lid 125 is hermetically sealed to the sidewalls124 using known techniques, such as welding (e.g., resistance welding,laser welding, etc.), soldering, etc. Hermetic sealing generally occursin the presence of inert gases as described above so that the resultingassembly is substantially free of reactive gases, such as oxygen orwater vapor.

It should be understood that the embodiments described are onlyexemplary, and that various other configurations may be employed in thepresent invention for hermetically sealing a capacitor element within ahousing. Referring to FIG. 2, for instance, another embodiment of acapacitor 200 is shown that employs a housing 222 that includes an outerwall 123 and a lid 225 between which a cavity 126 is formed thatincludes the capacitor element 120 and polymeric restraint 197. The lid225 includes an outer wall 223 that is integral with at least onesidewall 224. In the illustrated embodiment, for example, two opposingsidewalls 224 are shown in cross-section. The outer walls 223 and 123both extend in a lateral direction (−y direction) and are generallyparallel with each other and to the lateral direction of the anode lead6. The sidewall 224 extends from the outer wall 223 in a longitudinaldirection that is generally perpendicular to the outer wall 123. Adistal end 500 of the lid 225 is defined by the outer wall 223 and aproximal end 501 is defined by a lip 253 of the sidewall 224.

The lip 253 extends from the sidewall 224 in the lateral direction,which may be generally parallel to the lateral direction of the outerwall 123. The angle between the sidewall 224 and the lip 253 may vary,but is typically from about 60° to about 120°, in some embodiments fromabout 70° to about 110°, and in some embodiments, from about 80° toabout 100° (e.g., about) 90°. The lip 253 also defines a peripheral edge251, which may be generally perpendicular to the lateral direction inwhich the lip 253 and outer wall 123 extend. The peripheral edge 251 islocated beyond the outer periphery of the sidewall 224 and may begenerally coplanar with an edge 151 of the outer wall 123. The lip 253may be sealed to the outer wall 123 using any known technique, such aswelding (e.g., resistance or laser), soldering, glue, etc. For example,in the illustrated embodiment, a sealing member 287 is employed (e.g.,glass-to-metal seal, Kovar® ring, etc.) between the components tofacilitate their attachment. Regardless, the use of a lip describedabove can enable a more stable connection between the components andimprove the seal and mechanical stability of the capacitor.

Still other possible housing configurations may be employed in thepresent invention. For example, FIG. 3 shows a capacitor 300 having ahousing configuration similar to that of FIG. 2, except that terminalpins 327 b and 329 b are employed as the external terminations for theanode and cathode, respectively. More particularly, the terminal pin 327a extends through a trace 327 c formed in the outer wall 323 and isconnected to the anode lead 6 using known techniques (e.g., welding). Anadditional section 327 a may be employed to secure the pin 327 b.Likewise, the terminal pin 329 b extends through a trace 329 c formed inthe outer wall 323 and is connected to the cathode via a conductiveadhesive 133 as described above.

The embodiments shown in FIGS. 1-3 are discussed herein in terms of onlya single capacitor element. It should also be understood, however, thatmultiple capacitor elements may also be hermetically sealed within ahousing. The multiple capacitor elements may be attached to the housingusing any of a variety of different techniques. Referring to FIG. 4, forexample one particular embodiment of a capacitor 400 that contains twocapacitor elements is shown and will now be described in more detail.More particularly, the capacitor 400 includes a first capacitor element420 a in electrical communication with a second capacitor element 420 b.In this embodiment, the capacitor elements are aligned so that theirmajor surfaces are in a horizontal configuration. That is, a majorsurface of the capacitor element 420 a defined by its width (−xdirection) and length (−y direction) is positioned adjacent to acorresponding major surface of the capacitor element 420 b. Thus, themajor surfaces are generally coplanar. Alternatively, the capacitorelements may be arranged so that their major surfaces are not coplanar,but perpendicular to each other in a certain direction, such as the −zdirection or the −x direction. Of course, the capacitor elements neednot extend in the same direction.

The capacitor elements 420 a and 420 b are positioned within a housing422 that contains an outer wall 423 and sidewalls 424 and 425 thattogether define a cavity 426. Although not shown, a lid may be employedthat covers the upper surfaces of the sidewalls 424 and 425 and sealsthe assembly 400 as described above. Optionally, a polymeric restraintmay also be employed to help limit the vibration of the capacitorelements. In FIG. 4, for example, separate polymer restraints 497 a and497 b are positioned adjacent to and in contact with the capacitorelements 420 a and 420 b, respectively. The polymer restraints 497 a and497 b may be positioned in a variety of different locations. Further,one of the restraints may be eliminated, or additional restraints may beemployed. In certain embodiments, for example, it may be desired toemploy a polymeric restraint between the capacitor elements to furtherimprove mechanical stability.

In addition to the capacitor elements, the capacitor also contains ananode termination to which anode leads of respective capacitor elementsare electrically connected and a cathode termination to which thecathodes of respective capacitor elements are electrically connected.Referring again to FIG. 4, for example, the capacitor elements are shownconnected in parallel to a common cathode termination 429. In thisparticular embodiment, the cathode termination 429 is initially providedin a plane that is generally parallel to the bottom surface of thecapacitor elements and may be in electrical contact with conductivetraces (not shown). The capacitor 400 also includes connective members427 and 527 that are connected to anode leads 407 a and 407 b,respectively, of the capacitor elements 420 a and 420 b. Moreparticularly, the connective member 427 contains an upstanding portion465 and a planar portion 463 that is in connection with an anodetermination (not shown). Likewise, the connective 527 contains anupstanding portion 565 and a planar portion 563 that is in connectionwith an anode termination (not shown). Of course, it should beunderstood that a wide variety of other types of connection mechanismsmay also be employed. The present invention may be better understood byreference to the following examples.

Test Procedures Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency was 100 kHz andthe temperature was 23° C.±2° C.

Dissipation Factor

The dissipation factor may be measured using a Keithley 3330 PrecisionLCZ meter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak topeak sinusoidal signal. The operating frequency may be 120 Hz and thetemperature may be 23° C.±2° C.

Capacitance

The capacitance was measured using a Keithley 3330 Precision LCZ meterwith Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak to peaksinusoidal signal. The operating frequency was 120 Hz and thetemperature may be 23° C.±2° C. High temperature vacuum conditioning maybe conducted at a temperature of 180±5° C. and pressure 200 Pa in aninert atmosphere (e.g. argon). Whole conditioning cycle consists of aramp up phase during which target conditions are set up and hold phaseat the target temperature and pressure in an inert atmosphere. The timeperiod for the hold phase is 30 minutes. Capacitance is measured beforeand after conditioning with recovery time 15-30 minutes.

Leakage Current

Leakage current may be measured using a leakage test meter at atemperature of 23° C.±2° C. and at the rated voltage after a minimum of60 seconds.

EXAMPLE 1

40,000 μFV/g tantalum powder was used to form anode samples. Each anodesample was embedded with a tantalum wire, sintered at 1440° C., andpressed to a density of 5.1 g/cm³. The resulting pellets had a size of5.60×3.65×0.90 mm. The pellets were anodized to 71.0 volts inwater/phosphoric acid electrolyte with a conductivity of 8.6 mS at atemperature of 85° C. to form the dielectric layer. The pellets wereanodized again to 135 volts in a water/boric acid/disodium tetraboratewith a conductivity of 2.0 mS at a temperature of 30° C. for 25 secondsto form a thicker oxide layer built up on the outside. A conductivepolymer coating was then formed by dipping the anodes into a solution ofan intrinsically conductive thiophene polymer. Upon coating, the partswere dried at 125° C. for 15 minutes. This process was repeated 2 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 1.1% andviscosity 20 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 8 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content 2.0% andviscosity 20 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 3 times.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity 160 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 14 times. Theparts were then dipped into a graphite dispersion and dried. Finally,the parts were dipped into a silver dispersion and dried. Multiple parts(180) of 47 μF/35V capacitors were made in this manner.

EXAMPLE 2

Capacitors were formed in the manner described in Example 1, except thatafter anodization, the anode was dipped into a polyaniline solution asdescribed herein and then dried at 150° C. for 30 minutes. Subsequently,the composition was immersed in a solution containing sulfonic acid anddried at 150° C. for 30 minutes. Thereafter, the parts were dipped intoa solution of an intrinsically conductive thiophene polymer as describedherein. Upon coating, the parts were dried at 125° C. for 15 minutes.Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity 160 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 14 times. Theparts were then dipped into a graphite dispersion and dried. Finally,the parts were dipped into a silver dispersion and dried. Multiple parts(180) of 47 μF/35V capacitors were made in this manner.

EXAMPLE 3

Capacitors were formed in the manner described in Example 1, except thatafter anodization, the anode was dipped into a solution of anintrinsically conductive thiophene polymer as described herein. Uponcoating, the parts were dried at 125° C. for 15 minutes. Thereafter, theanode was dipped in an organic solution of polyaniline and dried at 150°C. for 30 minutes. Subsequently, the composition was immersed in asolution containing sulfonic acid and dried at 150° C. for 30 minutes.Thereafter, the parts were dipped into a solution of an intrinsicallyconductive thiophene polymer as described herein and dried at 125° C.for 15 minutes. Thereafter, the parts were dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity 160 mPa·s (Clevios™ K, Heraeus). Upon coating, the parts weredried at 125° C. for 15 minutes. This process was repeated 14 times. Theparts were then dipped into a graphite dispersion and dried. Finally,the parts were dipped into a silver dispersion and dried. Multiple parts(180) of 47 μF/35V capacitors were made in this manner.

The median results of capacitance before and after high temperaturevacuum conditioning are set forth below in Table 1.

TABLE 1 Capacitance Results Inner Initial Final Cathode Layers-capacitance capacitance Cycle Quantity (μF) (μF) Example 1 10 44.7544.31 Example 2 1 42.71 33.99 Example 3 2 46.25 44.37

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A solid electrolytic capacitor comprising acapacitor element, wherein the capacitor element comprises: a sinteredporous anode body; a dielectric that overlies the anode body; a solidelectrolyte that overlies the dielectric, wherein the solid electrolyteincludes a conductive polymer having repeating units derived from ananiline monomer having the following general formula (I):

wherein, R₅ and R₆ are independently hydrogen, alkyl, alkenyl, aryl,alkoxy, aryloxy, alkylthioalkyl, alkylaryl, arylalkyl, haloalkyl, amino,epoxy, silane, siloxane, alcohol, benzyl, carboxylate, ether, ethercarboxylate, ether sulfonate, ester sulfonate, urethane, or acombination thereof; and an external polymer coating that overlies thesolid electrolyte and includes conductive polymer particles.
 2. Thesolid electrolytic capacitor of claims 1, R₅ and R₆ are hydrogen.
 3. Thesolid electrolytic capacitor of claim 1, wherein the solid electrolytefurther includes a proton donor.
 4. The solid electrolytic capacitor ofclaim 3, wherein the proton donor is an organic acid compound.
 5. Thesolid electrolytic capacitor of claim 4, wherein the organic acidcompound has the following general formula (II):

wherein, m is an integer from 1 to 10; M is hydrogen, an organic freeradical group, an inorganic free radical group, or a combinationthereof; X is an anion; R⁴, R⁵, and R⁶ are independently hydrogen, ahydrocarbon group or a R⁹ ₃Si— group, wherein R⁹ are each independentlyhydrogen or a hydrocarbon group; and R⁷ and R⁸ are independently ahydrocarbon group or —(R¹⁰O)_(q)—R¹¹, wherein q is an integer equal to 1or more, R¹⁰ is a hydrocarbon group or a silylene group, R¹¹ ishydrogen, hydrocarbon group, or R¹² ₃Si—, wherein R¹² are eachindependently a hydrocarbon group.
 6. The solid electrolytic capacitorof claim 5, wherein M is an alkali metal.
 7. The solid electrolyticcapacitor of claim 5, wherein X is SO₃.
 8. The solid electrolyticcapacitor of claim 5, wherein R⁴, R⁵, and R⁶ are each hydrogen.
 9. Thesolid electrolytic capacitor of claim 5, wherein R⁷ and R⁸ areindependently a straight-chain or branched C₁-C₂₄ alkyl.
 10. The solidelectrolytic capacitor of claim 1, wherein the solid electrolyte furtherincludes an external dopant.
 11. The solid electrolytic capacitor ofclaim 10, wherein the external dopant is a hydroxphenolic compoundhaving one of the following structures (III), (IV), (V), or (VI):

wherein, n is an integer of 0 to 5; and R is independently a C₁-C₂₀alkyl, alkenyl, cycloalkyl, aryl, alkylaryl, or a combination thereof.12. The solid electrolytic capacitor of claim 10, wherein the externaldopant includes methoxyphenol, ethoxyphenol, propoxyphenol,isopropoxyphenol, butyloxyphenol, isobutyloxyphenol,tert-butyloxyphenol, hydroxynaphthalene, cresol, ethylphenol,propylphenol, butylphenol, pentylphenol, 1,6-naphthanediol,2,6-naphthalenediol, 2,7-naphthalenediol, or a combination thereof. 13.The solid electrolytic capacitor of claim 1, wherein the solidelectrolyte further includes a heat stabilizer.
 14. The solidelectrolytic capacitor of claim 13, wherein the heat stabilizer includesan organic acid.
 15. The solid electrolytic capacitor of claim 1,wherein the solid electrolyte contains at least one inner layer thatincludes the conductive polymer.
 16. The solid electrolytic capacitor ofclaim 1, wherein the solid electrolyte contains at least outer layer.17. The solid electrolytic capacitor of claim 16, wherein the outerlayer is formed from particles that contain a thiophene polymer.
 18. Thesolid electrolytic capacitor of claim 16, wherein the outer layercontains a hydroxyl-functional nonionic polymer.
 19. The solidelectrolytic capacitor of claim 1, wherein the conductive polymerparticles in the external polymer coating include a thiophene polymer.20. The solid electrolytic capacitor of claim 1, wherein the externalpolymer coating further comprises a crosslinking agent.
 21. The solidelectrolytic capacitor of claim 1, wherein the conductive polymerparticles in the external polymer coating have an average size of fromabout 80 to about 600 nanometers.
 22. The solid electrolytic capacitorof claim 1, further comprising an anode lead extending from thecapacitor element.
 23. The solid electrolytic capacitor of claim 23,further comprising an anode termination that is in electrical contactwith the anode lead and a cathode termination that is in electricalconnection with the solid electrolyte.
 24. The solid electrolyticcapacitor of claim 1, further comprising a housing within which thecapacitor element is enclosed.
 25. The solid electrolytic capacitor ofclaim 24, wherein the housing is formed from a resinous material thatencapsulates the capacitor element.
 26. The solid electrolytic capacitorof claim 24, wherein the housing defines an interior cavity within whichthe capacitor element is positioned, wherein the interior cavity has agaseous atmosphere.
 27. The solid electrolytic capacitor of claim 1,wherein the anode body includes tantalum.
 28. The solid electrolyticcapacitor of claim 1, wherein the capacitor element further comprises acathode coating that contains a metal particle layer that overlies thesolid electrolyte, wherein the metal particle layer includes a pluralityof conductive metal particles.